1. Field of the Invention
The present invention relates to a key telephone exchange system, and in particular, to a method for designating a pair of key telephone sets to make an automatic call therebetween in an idle state of the key telephone sets.
2. Description of the Related Art
In a conventional key telephone exchange system, a user of a key telephone set should dial a telephone number for a specified extension line subscriber every time when making a call to the specified extension line subscriber. Further, when the extension line is engaged by the user for a long time, the other extension line subscribers cannot call the user of the key telephone set. An example of a keytelephone system having an intercome feature is disclosed in U.S. Pat. No. 3,976,847 to Richard Henry Bidlac, et al. entitled Key Telephone System Intercom Arrangement.
In order to solve the above shortcoming of the prior art key telephone exchange system, Korean patent application No. 96-19234, filed by the applicant of this application, see U.S. patent application Ser. No. 08/867,688, discloses a method for making an automatic call. The proposed key telephone exchange system, however, can designate only a single pair of the key telephone sets. That is, since the pair of key telephone sets to be provided with the automatic call service is previously determined, the user of the key telephone needs to ask a telephone technician for help in order to change the extension line subscriber to be provided with the automatic call service.